82 IOWA ACADEMY OF SCIENCE 



Moines, 1895. At this time the areal work of the Iowa Geological Sur- 

 vey had hardly been begun. Reports on but two counties had been pub- 

 lished. The judgment of Keyes expressed in the paper cited that "the 

 apparent rareness heretofore of glacial striations in Iowa is manifestly 

 due not so much to an absence of ice action as it is to a lack of careful 

 observation and examination," may well have been accepted by the 

 entire staff of the survey and they may have entered upon their work 

 with confident expectation that a thorough search would multiply many 

 fold the discovered autographs written by pleistocene glaciers upon the 

 rocks of Iowa. 



During the sixteen years which have elapsed since the publication of 

 Keyes' paper, the areal survey of the state has been in progress and is 

 now well nigh completed. Thousands of quarries and outcrops have 

 been examined but the list of glacial scorings complete to date, so far as 

 the writer is able to ascertain, remains a meagre one. Only eleven new 

 localities have been added to the eight of Keyes' paper, and several of 

 these are either in the same district or adjoin localities reported by 

 Keyes. 



The rarity of glacial scorings in Iowa is therefore not merely appar- 

 ent. It is real. Giving all due weight to "the illusory effects due to 

 lack of observation on account of deep drift covering," it still remains 

 that ice-scorings are relatively rare in Iowa. Indeed, it is largely due 

 to the covering of till that the list of scorings is as large as it is, for it 

 is only the cover of impervious clays which has prevented post glacial 

 obliteration. 



From the fact that careful search has found glaciated rock surfaces in 

 but ten counties of the state, we may infer that the pleistocene ice sheets 

 which so strongly scoured the rocks of more northern areas here did 

 little abrasive work. The deep residual clays which covered the state 

 with a ' ' terra rossa ' ' in late Tertiary times were partially but not wholly 

 scraped away. Remnants may now be found in almost any quarry 

 resting on rock surfaces more or less decayed and pitted by the solvent 

 action of descending ground waters. That the larger part of this decay 

 is preglacial may be inferred from the thickness of the weathered zone 

 of the rock, from the size of solution pipes, from the depth of geest occa- 

 sionally found, and from the close similarity of these diagnostic features 

 to the phenomena of weathering to be observed in the driftless area. 

 Still surer evidence of preglacial rock-decay is found in sections show- 

 ing masses of partially decayed rock with the geest still in place upon 

 them which have been plucked and are now found imbedded in till. 

 Iowa appears to have been an area of glacial deposition rather than an 



